Effects of temperature and microbial disruption on juvenile kelp Ecklonia radiata and its associated bacterial community

Ocean warming can affect the development and physiological responses of kelps, and under future climate change scenarios, increasing seawater temperatures pose a major threat to these habitat-forming species. However, little is known about the effects of warming on epiphytic bacterial communities and how an altered microbiome may interact with temperature stress, affecting the condition and survival of kelp, particularly of the potentially more vulnerable early life stages. Here, we tested the effects of thermal stress on the growth and physiological responses of juvenile kelp Ecklonia radiata in which their epiphytic bacterial community was experimentally disrupted using antimicrobials, simulating dysbiosis. We hypothesized that, under thermal stress (23°C, simulating a extreme scenario of ocean warming in Tasmania), kelp with a disrupted bacterial community would be more strongly affected than kelp with an undisrupted microbiome or kelp under ambient temperature (14°C) but with a disrupted microbiota. Thermal stress reduced growth, increased tissue bleaching and negatively affected net photosynthesis of kelp. In addition, a substantial change in the epiphytic bacterial community structure was also found under thermal stress conditions, with an increase in the abundance of potentially pathogenic bacterial groups. However, microbial disruption did not act synergistically with thermal stress to affect kelp juveniles. These results suggest that effects of elevated temperature on juvenile kelps is not microbially-mediated and that juveniles may be less susceptible to disruptions of their microbiome

Host genotype and microbiome associations in co-occurring clonal and non-clonal kelp, Ecklonia radiata

A fundamental question in holobiont biology is the extent to which microbiomes are determined by host characteristics regulated by their genotype. Studies on the interactions of host genotype and microbiomes are emerging but disentangling the role that host genotype has in shaping microbiomes remains challenging in natural settings. Host genotypes tend to be segregated in space and affected by different environments. Here we overcome this challenge by studying an unusual situation where host asexual (5 clonal lineages) and sexual genotypes (15 non-clonal lineages) of the same species co-occur under the same environment. This allowed us to partition the influence of morphological traits and genotype in shaping host-associated bacterial communities. Lamina-associated bacteria of co-occurring kelp sexual non-clonal (Ecklonia radiata) and asexual clonal (E. brevipes) morphs were compared to test whether host genotype influences microbiomes beyond morphology. Similarity of bacterial composition and predicted functions were evaluated among individuals within a single clonal genotype or among non-clonal genotypes of each morph. Higher similarity in bacterial composition and inferred functions were found among identical clones of E. brevipes compared to other clonal genotypes or unique non-clonal E. radiata genotypes. Additionally, bacterial diversity and composition differed significantly between the two morphs and were related with one morphological trait in E. brevipes (haptera). Thus, factors regulated by the host genotype (e.g. secondary metabolite production) likely drive differences in microbial communities between morphs. The strong association of genotype and microbiome found here highlights the importance of genetic relatedness of hosts in determining variability in their bacterial symbionts.publishedVersio

Spatial variation in microbial communities associated with sea-ice algae in Commonwealth Bay, East Antarctica

Antarctic sea-ice forms a complex and dynamic system that drives many ecological processes in the Southern Ocean. Sea-ice microalgae and their associated microbial communities are understood to influence nutrient flow and allocation in marine polar environments. Sea-ice microalgae and their microbiota can have high seasonal and regional (>1000 km2) compositional and abundance variation, driven by factors modulating their growth, symbiotic interactions and function. In contrast, our knowledge of small-scale variation in these communities is limited. Understanding variation across multiple scales and its potential drivers is critical for informing on how multiple stressors impact sea-ice communities and the functions they provide. Here, we characterized bacterial communities associated with sea-ice microalgae and the potential drivers that influence their variation across a range of spatial scales (metres to >10 kms) in a previously understudied area in Commonwealth Bay, East Antarctica where anomalous events have substantially and rapidly expanded local sea-ice coverage. We found a higher abundance and different composition of bacterial communities living in sea-ice microalgae closer to the shore compared to those further from the coast. Variation in community structure increased linearly with distance between samples. Ice thickness and depth to the seabed were found to be poor predictors of these communities. Further research on the small-scale environmental drivers influencing these communities is needed to fully understand how large-scale regional events can affect local function and ecosystem processes

Spatial compositional turnover varies with trophic level and body size in marine assemblages of micro- and macroorganisms

Abstract Aim Spatial compositional turnover varies considerably among co-occurring assemblages of organisms, presumably shaped by common processes related to species traits. We investigated patterns of spatial turnover in a diverse set of marine assemblages using zeta diversity, which extends traditional pairwise measures of turnover to capture the roles of both rare and common species in shaping assemblage turnover. We tested the generality of hypothesized patterns related to ecological traits and provide insights into mechanisms of biodiversity change. Location Temperate pelagic and benthic marine assemblages of micro- and macroorganisms along south-eastern Australia (30–36° S latitude). Time period 2008–2021. Major taxa studied Bacteria, phytoplankton, zooplankton, fish, and macrobenthic groups. Methods Six marine datasets spanning bacteria to fishes were collated for measures of “species” occurrence, with a 1° latitude grain. For each assemblage, ecological traits of body size, habitat and trophic level were analysed for the form and rate of decline in zeta diversity and for the species retention rate. Results Species at higher trophic levels showed two to three times the rate of zeta diversity decline compared with lower trophic levels, indicating an increase in turnover from phytoplankton to carnivorous fishes. Body size showed the hypothesized unimodal relationship with rates of turnover for macroorganisms. Patterns of bacterial turnover contrasted with those found for macroorganisms, with the highest levels of turnover in pelagic habitats compared with benthic (kelp-associated) habitats. The shape of retention rate curves showed the importance of both rare and common species in driving turnover; a finding that would not have been observable using pairwise (beta diversity) measures of turnover. Main conclusions Our results support theoretical predictions for phytoplankton and macroorganisms, showing an increase in turnover rate with trophic level, but these predictions did not hold for bacteria. Such deviations from theory need to be investigated further to identify underlying processes that govern microbial assemblage dynamics

A multilevel assessment of sediment bioremediation with bioturbating macrofauna

Estuaries and coastal intertidal environments supply important ecosystem services and resources. Within these systems, sediments play a crucial role in processing organic inputs and providing nutrients for local food webs. Benthic macrofauna and sediment microbial communities participate actively in these processes and can interact to influence overall ecosystem function. Through different bioturbation processes, macrofauna can affect biogeochemical cycling in sediments and influence microbial communities. However, anthropogenic derived eutrophication has increased globally in recent years and has been found to negatively impact these systems. Excess inputs of anthropogenic contaminants can disrupt key sediment processes involving macrofauna and microbial communities. Current options for sediment remediation are costly and may result in further impacts on communities. An alternative method for sediment bioremediation involves the application of macrofaunal bioturbators to stimulate microbial processes including contaminant removal. However, to confidently apply such an alternative requires clarity on the effect of macrofauna on contaminants, the contaminant concentrations at which macrofauna will actively affect the sediments, the potential effects of bioturbators on microbial communities, and whether these applications can be applied in situ at large scales. Here I used a systematic review and meta-analysis to analyse current knowledge on the effect of bioturbating macrofauna on contaminants and quantify how this interaction changes depending on relevant biotic and abiotic variables. Secondly, I used an experimental approach with sediment mesocosms to further explore the contaminant thresholds for effective remediation by macrofauna bioturbation and interactions with microbial communities in highly enriched sediments. Finally, a large-scale field experiment was done to explore the influence in situ nitrogen enrichment on microbial communities in the sediment and within macrofauna burrows under variable environmental contexts. The combined results here demonstrate that the effect of macrofauna bioturbation on stimulating bacterial communities in organically enriched sediments is highly taxa driven and additional factors such as macrofauna intraspecific variations in body size, temperature, animal density, magnitude of contamination and site specific organic matter content need to be considered for potential bioremediation and coastal management plans

DataSheet_1_Effects of temperature and microbial disruption on juvenile kelp Ecklonia radiata and its associated bacterial community.docx

Ocean warming can affect the development and physiological responses of kelps, and under future climate change scenarios, increasing seawater temperatures pose a major threat to these habitat-forming species. However, little is known about the effects of warming on epiphytic bacterial communities and how an altered microbiome may interact with temperature stress, affecting the condition and survival of kelp, particularly of the potentially more vulnerable early life stages. Here, we tested the effects of thermal stress on the growth and physiological responses of juvenile kelp Ecklonia radiata in which their epiphytic bacterial community was experimentally disrupted using antimicrobials, simulating dysbiosis. We hypothesized that, under thermal stress (23°C, simulating a extreme scenario of ocean warming in Tasmania), kelp with a disrupted bacterial community would be more strongly affected than kelp with an undisrupted microbiome or kelp under ambient temperature (14°C) but with a disrupted microbiota. Thermal stress reduced growth, increased tissue bleaching and negatively affected net photosynthesis of kelp. In addition, a substantial change in the epiphytic bacterial community structure was also found under thermal stress conditions, with an increase in the abundance of potentially pathogenic bacterial groups. However, microbial disruption did not act synergistically with thermal stress to affect kelp juveniles. These results suggest that effects of elevated temperature on juvenile kelps is not microbially-mediated and that juveniles may be less susceptible to disruptions of their microbiome.</p

Effect of seaweed canopy disturbance on understory microbial communities on rocky shores

Introduction The collapse of macroalgal habitats is altering the structure of benthic communities on rocky shores globally. Nonetheless, how the loss of canopy-forming macroalgae influences the structure of epilithic microbial communities is yet to be explored.Methods Here, we used experimental field manipulations and 16S-rRNA-gene amplicon sequencing to determine the effects of macroalgal loss on the understory bacterial communities and their relationship with epiphytic bacteria on macroalgae. Beds of the fucoid Hormosira banksii were exposed to different levels of disturbance resulting in five treatments: (i) 100% removal of Hormosira individuals, (ii) 50% removal, (iii) no removal, (iv) a procedural control that mimicked the removal process, but no Hormosira was removed and (v) adjacent bare rock. Canopy cover, bacterial communities (epilithic and epiphytic) and benthic macroorganisms were monitored for 16 months.Results Results showed that reductions in canopy cover rapidly altered understory bacterial diversity and composition. Hormosira canopies in 50% and 100% removal plots showed signs of recovery over time, but understory epilithic bacterial communities remained distinct throughout the experiment in plots that experienced full Hormosira removal. Changes in bacterial communities were not related to changes in other benthic macroorganisms.Discussion These results demonstrate that understory epilithic bacterial communities respond rapidly to environmental disturbances at small scales and these changes can be long-lasting. A deeper knowledge of the ecological role of understory epilithic microbial communities is needed to better understand potential cascading effects of disturbances on the functioning of macroalgal-dominated systems